A raglan shirt with the words "SUGOI DEKAI" written on the chest. "Sugoi dekai" means "super huge".
The shirt was originally worn by Uzaki Hana from Uzaki-chan Wa Asobitai!, but it became meme attire after the anime adaptation was released. Other characters wearing the shirt shouldn't be tagged as Uzaki Hana, unless they're specifically cosplaying her.